1. Field of the Invention
The present invention generally relates to a map data selection supporting device, and more particularly to a device which helps a user more easily select desired map data from a map data group. The present invention also relates to a map data processing system which incorporates the map data selection supporting device of the present invention. The map data processing system comprises an information center and a terminal device. The information center and the terminal device are connected to each other via a communication means so that the former sends the latest map data to the latter. Using the latest map data, the terminal device updates map data stored therein.
The present invention is particularly applicable to a map data processing system in which a terminal device is mounted on a moving body. In the following, a vehicle will be taken as an example of a moving body.
2. Description of the Related Art
The use of map data inside a moving body has become more popular as navigation systems have spread. In order to use map data inside a vehicle, the vehicle must carry a map data storing device for storing map data. Map data concerning areas around a present or destination position is read from the device and displayed. In the storing device is also stored map data to be used in searching for an optimum route from the present position to the destination position, and in map-matching for detecting the precise present position.
A conventional map data storing device generally requires a large capacity memory medium, such as a CD-ROM, on which is stored fixed map data. In order to update the stored data, the entire medium must be exchanged.
Meanwhile, a data communication systems have been developed. In the most common system, a vehicle communicates with an information center via a communication means. Typical examples of such a system are Vehicle Information and Communication System (VICS) and Intelligent Transport System (ITS).
Accompanying the development of such a data communication system, a map data processing system (a maintenance system) has also been proposed, in which map data held on a vehicle side is updated utilizing data communication. Specifically, a terminal device mounted on a vehicle carries a read/write map data storing device (medium), and updates the map data held in the storing device using the latest map data obtained from an information center. With this system, a user can access the latest map data without exchanging a CD-ROM. One example of the above system is disclosed by Japanese Patent Laid-Open No. Hei 7-262493.
In general, a number of maps on different reduced scales are available in such a map data processing system. There are a number of divided smaller sectional maps for each scale, and map data is stored for each sectional map. That is, the map data storing device stores map data of maps with a large coverage in the form of a collection of sectional map data (a map data group).
In a map data updating process using data communication, sectional map data is individually processed. This advantageously enables to update desired sectional map data only, though it disadvantageously leaves updated map data in different versions stored disorderly in a map data storing device. It is difficult for a user to manage and update as necessary map data stored in such a condition, especially if the vehicle operator is not well accustomed to data management as a user of a general-purpose personal computer. Further, management of map data of a large volume may be difficult to perform by operating such a device that is generally equipped to a vehicle with a limited inside space. Considering the above, it is not preferable that a user be required to follow a complicated procedure. Therefore, a simpler process for managing and updating map data has been desired. Otherwise, the following problems, for example, will be expected.
(i) In a map data updating process, in order to exploit the advantage of individual updating of sectional map data, a user is required to select desired sectional map data to be updated (updating map data) from a map data group. The selected map data is rendered into subsequent process. To help the user's selection, a map data selection supporting device is provided. In this device, when a user designates a selection condition (parameter), sectional map data which meet the parameter is selected from a map data group stored in the map data storing device. A selection condition must be distinct enough to specify particular sectional map data.
With a conventional device, such as the one disclosed in the above JP Laid-open No. Hei 7-262493, a user is required to select at least "region" as a selection condition. Thus, in order to select "region," the user inputs the name of a desired regional unit, such as a prefecture in Japan or a state or city in the U.S.
However, when considering updating a map, a user tends to think of a map to be updated in connection with a particular point. For example, he/she may wish to update a map of areas around his/her present position, his/her home or garage, or a destination. Therefore, conventionally, the user must first judge which area, or a regional unit, includes the particular point in mind in order to designate appropriate "region." Making such judgement, however, may be troublesome. Worse, the user may not always know for sure a correct name of an area or a regional unit which includes a particular point.
(ii) Designation of an improper selection condition may likely lead to the selection of map data having too large or small map data volume. For example, designation of too wide an area causes map data having too large a volume to be selected, while designation of too small an area causes selection of map data having too small volume. A too large data volume may increase a processing load, in particular, a load for communication with an information center. Note that a vehicle may travel in areas with tunnels or overpasses. Such a vehicle may be able to communicate with an information center in a preferable condition, i.e., without disturbance by, for example, a building, for only a limited time due to bad communication condition. Map data having a very large data volume may take a longer time to be fully transmitted than such a limited time which ensures preferable communication condition. On the other hand, selection of map data having too small a data volume is wasteful because the performance of system is not fully utilized.
In order to avoid these problems, a user is required to designate a selection condition that leads to selection of map data having an appropriate data volume. This, however, is difficult for a user to achieve as he/she may not be sufficiently informed to make a judgement concerning data volume.
(iii) Conventionally, a user has no way to know the current status in terms of newness of map data corresponding to a selection condition which he/she intends to input via a selection supporting device. That is, it may often be a case that selected map data has already been updated partly or entirely. Therefore, it has conventionally been difficult for a user to designate an appropriate selection condition due to lack of information.